# Code dedicated to the computation and properties of "stable ranges"
#
# These stable ranges are use for obsolescence markers discovery
#
# Copyright 2017 Pierre-Yves David <pierre-yves.david@ens-lyon.org>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

import collections
import math

from mercurial import (
    commands,
    cmdutil,
    localrepo,
    node as nodemod,
    scmutil,
)

from mercurial.i18n import _

from . import (
    exthelper,
)

eh = exthelper.exthelper()

##################################
### Stable topological sorting ###
##################################
@eh.command(
    'debugstablesort',
    [
        ('', 'rev', [], 'heads to start from'),
    ] + commands.formatteropts,
    _(''))
def debugstablesort(ui, repo, **opts):
    """display the ::REVS set topologically sorted in a stable way
    """
    revs = scmutil.revrange(repo, opts['rev'])
    displayer = cmdutil.show_changeset(ui, repo, opts, buffered=True)
    for r in stablesort(repo, revs):
        ctx = repo[r]
        displayer.show(ctx)
        displayer.flush(ctx)
    displayer.close()

def stablesort(repo, revs, mergecallback=None):
    """return '::revs' topologically sorted in "stable" order

    This is a depth first traversal starting from 'nullrev', using node as a
    tie breaker.
    """
    # Various notes:
    #
    # * Bitbucket is used dates as tie breaker, that might be a good idea.
    #
    # * It seemds we can traverse in the same order from (one) head to bottom,
    #   if we the following record data for each merge:
    #
    #  - highest (stablesort-wise) common ancestors,
    #  - order of parents (tablesort-wise)
    cl = repo.changelog
    parents = cl.parentrevs
    nullrev = nodemod.nullrev
    n = cl.node
    # step 1: We need a parents -> children mapping for 2 reasons.
    #
    # * we build the order from nullrev to tip
    #
    # * we need to detect branching
    children = collections.defaultdict(list)
    for r in cl.ancestors(revs, inclusive=True):
        p1, p2 = parents(r)
        children[p1].append(r)
        if p2 != nullrev:
            children[p2].append(r)
    # step two: walk back up
    # * pick lowest node in case of branching
    # * stack disregarded part of the branching
    # * process merge when both parents are yielded

    # track what changeset has been
    seen = [0] * (max(revs) + 2)
    seen[-1] = True # nullrev is known
    # starts from repository roots
    # reuse the list form the mapping as we won't need it again anyway
    stack = children[nullrev]
    if not stack:
        return []
    if 1 < len(stack):
        stack.sort(key=n, reverse=True)

    # list of rev, maybe we should yield, but since we built a children mapping we are 'O(N)' already
    result = []

    current = stack.pop()
    while current is not None or stack:
        if current is None:
            # previous iteration reached a merge or an unready merge,
            current = stack.pop()
            if seen[current]:
                current = None
                continue
        p1, p2 = parents(current)
        if not (seen[p1] and seen[p2]):
            # we can't iterate on this merge yet because other child is not
            # yielded yet (and we are topo sorting) we can discard it for now
            # because it will be reached from the other child.
            current = None
            continue
        assert not seen[current]
        seen[current] = True
        result.append(current) # could be yield, cf earlier comment
        if mergecallback is not None and p2 != nullrev:
            mergecallback(result, current)
        cs = children[current]
        if not cs:
            current = None
        elif 1 == len(cs):
            current = cs[0]
        else:
            cs.sort(key=n, reverse=True)
            current = cs.pop() # proceed on smallest
            stack.extend(cs)   # stack the rest for later
    assert len(result) == len(set(result))
    return result

#################################
### Stable Range computation  ###
#################################

def _hlp2(i):
    """return highest power of two lower than 'i'"""
    return 2 ** int(math.log(i - 1, 2))

def subrangesclosure(repo, heads):
    """set of all standard subrange under heads

    This is intended for debug purposes. Range are returned from largest to
    smallest in terms of number of revision it contains."""
    subranges = repo.stablerange.subranges
    toproceed = [(r, 0, ) for r in heads]
    ranges = set(toproceed)
    while toproceed:
        entry = toproceed.pop()
        for r in subranges(repo, entry):
            if r not in ranges:
                ranges.add(r)
                toproceed.append(r)
    ranges = list(ranges)
    n = repo.changelog.node
    rangelength = repo.stablerange.rangelength
    ranges.sort(key=lambda r: (-rangelength(repo, r), n(r[0])))
    return ranges

class stablerange(object):

    def __init__(self):
        self._depthcache = {}
        self._subrangescache = {}

        # To slices merge, we need to walk their descendant in reverse stable
        # sort order. For now we perform a full stable sort their descendant
        # and then use the relevant top most part. This order is going to be
        # the same for all ranges headed at the same merge. So we cache these
        # value to reuse them accross the same invocation.
        self._stablesortcache = {}
        # something useful to compute the above
        # mergerev -> stablesort, length
        self._stablesortprepared = {}
        # caching parent call # as we do so many of them
        self._parentscache = {}

    def warmup(self, repo, heads):
        """warm the cache up to 'heads'"""
        repo = repo.unfiltered()
        for r in repo.revs("::%ld", heads):
            self.depthrev(repo, r)

    def depthrev(self, repo, rev):
        repo = repo.unfiltered()
        cl = repo.changelog
        cache = self._depthcache
        nullrev = nodemod.nullrev
        stack = [rev]
        while stack:
            revdepth = None
            current = stack[-1]
            revdepth = cache.get(current)
            if revdepth is not None:
                stack.pop()
                continue
            p1, p2 = self._parents(current, cl.parentrevs)
            if p1 == nullrev:
                # root case
                revdepth = 1
            elif p2 == nullrev:
                # linear commit case
                parentdepth = cache.get(p1)
                if parentdepth is None:
                    stack.append(p1)
                else:
                    revdepth = parentdepth + 1
            else:
                # merge case
                revdepth = self._depthmerge(cl, current, p1, p2, stack, cache)
            if revdepth is not None:
                cache[current] = revdepth
                stack.pop()
        # actual_depth = len(list(cl.ancestors([rev], inclusive=True)))
        # assert revdepth == actual_depth, (rev, revdepth, actual_depth)
        return revdepth

    def rangelength(self, repo, rangeid):
        headrev, index = rangeid[0], rangeid[1]
        return self.depthrev(repo, headrev) - index

    def subranges(self, repo, rangeid):
        cached = self._subrangescache.get(rangeid)
        if cached is not None:
            return cached
        value = self._subranges(repo, rangeid)
        self._subrangescache[rangeid] = value
        return value

    def revsfromrange(self, repo, rangeid):
        headrev, index = rangeid
        rangelength = self.rangelength(repo, rangeid)
        if rangelength == 1:
            revs = [headrev]
        else:
            # get all revs under heads in stable order
            #
            # note: In the general case we can just walk down and then request
            # data about the merge. But I'm not sure this function will be even
            # call for the general case.
            allrevs = self._stablesortcache.get(headrev)
            if allrevs is None:
                allrevs = self._getrevsfrommerge(repo, headrev)
                if allrevs is None:
                    allrevs = stablesort(repo, [headrev],
                                         mergecallback=self._filestablesortcache)
                self._stablesortcache[headrev] = allrevs
            # takes from index
            revs = allrevs[index:]
        # sanity checks
        assert len(revs) == rangelength
        return revs

    def _parents(self, rev, func):
        parents = self._parentscache.get(rev)
        if parents is None:
            parents = func(rev)
            self._parentscache[rev] = parents
        return parents

    def _filestablesortcache(self, sortedrevs, merge):
        if merge not in self._stablesortprepared:
            self._stablesortprepared[merge] = (sortedrevs, len(sortedrevs))

    def _getrevsfrommerge(self, repo, merge):
        prepared = self._stablesortprepared.get(merge)
        if prepared is None:
            return None

        mergedepth = self.depthrev(repo, merge)
        allrevs = prepared[0][:prepared[1]]
        nbextrarevs = prepared[1] - mergedepth
        if not nbextrarevs:
            return allrevs

        anc = repo.changelog.ancestors([merge], inclusive=True)
        top = []
        counter = nbextrarevs
        for rev in reversed(allrevs):
            if rev in anc:
                top.append(rev)
            else:
                counter -= 1
                if counter <= 0:
                    break

        bottomidx = prepared[1] - (nbextrarevs + len(top))
        revs = allrevs[:bottomidx]
        revs.extend(reversed(top))
        return revs

    @staticmethod
    def _depthmerge(cl, rev, p1, p2, stack, cache):
        # sub method to simplify the main 'depthrev' one
        revdepth = None
        depth_p1 = cache.get(p1)
        depth_p2 = cache.get(p2)
        missingparent = False
        if depth_p1 is None:
            stack.append(p1)
            missingparent = True
        if depth_p2 is None:
            stack.append(p2)
            missingparent = True
        if missingparent:
            return None
        # computin depth of a merge
        # XXX the common ancestors heads could be cached
        ancnodes = cl.commonancestorsheads(cl.node(p1), cl.node(p2))
        ancrevs = [cl.rev(a) for a in ancnodes]
        anyunkown = False
        ancdepth = []
        for r in ancrevs:
            d = cache.get(r)
            if d is None:
                anyunkown = True
                stack.append(r)
            ancdepth.append((r, d))
        if anyunkown:
            return None
        if not ancrevs:
            # unrelated branch, (no common root)
            revdepth = depth_p1 + depth_p2 + 1
        elif len(ancrevs) == 1:
            # one unique branch point:
            # we can compute depth without any walk
            depth_anc = ancdepth[0][1]
            revdepth = depth_p1 + (depth_p2 - depth_anc) + 1
        else:
            # multiple ancestors, we pick one that is
            # * the deepest (less changeset outside of it),
            # * lowest revs because more chance to have descendant of other "above"
            anc, revdepth = max(ancdepth, key=lambda x: (x[1], -x[0]))
            revdepth += len(cl.findmissingrevs(common=[anc], heads=[rev]))
        return revdepth

    def _subranges(self, repo, rangeid):
        if self.rangelength(repo, rangeid) == 1:
            return []
        slicepoint = self._slicepoint(repo, rangeid)

        # make sure we have cache for all relevant parent first to prevent
        # recursion (python is bad with recursion
        stack = []
        current = rangeid
        while current is not None:
            current = self._cold_reusable(repo, current, slicepoint)
            if current is not None:
                stack.append(current)
        while stack:
            # these call will directly compute the subranges
            self.subranges(repo, stack.pop())
        return self._slicesrangeat(repo, rangeid, slicepoint)

    def _cold_reusable(self, repo, rangeid, slicepoint):
        """return parent range that it would be useful to prepare to slice
        rangeid at slicepoint

        This function also have the important task to update the revscache of
        the parent revs if possible and needed"""
        # is this is a merge, there is not need to prepare the parents.
        p1, p2 = self._parents(rangeid[0], repo.changelog.parentrevs)
        if p2 != nodemod.nullrev:
            return None
        reusablerev = p1
        # if we reached the slicepoint, no need to go further
        if self.depthrev(repo, reusablerev) <= slicepoint:
            return None

        reurange = (reusablerev, rangeid[1])
        # if we have an entry for the current range, lets update the cache
        # if we already have subrange for this range, no need to prepare it.
        if self._subrangescache.get(reurange) is not None:
            return None

        # look like we found a relevent parentrange with no cache yet
        return reurange

    def _slicepoint(self, repo, rangeid):
        rangedepth = self.depthrev(repo, rangeid[0])
        step = _hlp2(rangedepth)
        standard_start = 0
        while standard_start < rangeid[1] and 0 < step:
            if standard_start + step < rangedepth:
                standard_start += step
            step //= 2
        if rangeid[1] == standard_start:
            slicesize = _hlp2(self.rangelength(repo, rangeid))
            slicepoint = rangeid[1] + slicesize
        else:
            assert standard_start < rangedepth
            slicepoint = standard_start
        return slicepoint

    def _slicesrangeat(self, repo, rangeid, globalindex):
        p1, p2 = self._parents(rangeid[0], repo.changelog.parentrevs)
        if p2 != nodemod.nullrev:
            return self._slicesrangeatmerge(repo, rangeid, globalindex)

        reuserev = p1

        assert reuserev != nodemod.nullrev

        reuserange = (reuserev, rangeid[1])
        top = (rangeid[0], globalindex)

        if rangeid[1] + self.rangelength(repo, reuserange) == globalindex:
            return [reuserange, top]
        # This will not initiate a recursion since we took appropriate
        # precaution in the caller of this method to ensure it will be so.
        # It the parent is a merge that will not be the case but computing
        # subranges from a merge will not recurse.
        reusesubranges = self.subranges(repo, reuserange)
        slices = reusesubranges[:-1] # pop the top
        slices.append(top)
        return slices

    def _slicesrangeatmerge(self, repo, rangeid, globalindex):
        localindex = globalindex - rangeid[1]
        cl = repo.changelog

        result = []
        allrevs = self.revsfromrange(repo, rangeid)
        bottomrevs = allrevs[:localindex]

        if globalindex == self.depthrev(repo, bottomrevs[-1]):
            # simple case, top revision in the bottom set contains exactly the
            # revision we needs
            result.append((bottomrevs[-1], rangeid[1]))
        else:
            parentrevs = cl.parentrevs
            parents = self._parents
            bheads = set(bottomrevs)
            du = bheads.difference_update
            reachableroots = repo.changelog.reachableroots
            for r in bottomrevs:
                du(parents(r, parentrevs))
            for h in bheads:
                # reachable roots is fast because is C
                #
                # It is worth noting that will use this kind of filtering from
                # "h" multiple time in a warming run. So using "ancestors" and
                # caching that should be faster. But python code filtering on
                # the ancestors end up being slower.
                hrevs = reachableroots(bottomrevs[0], [h], bottomrevs, True)
                start = self.depthrev(repo, h) - len(hrevs)
                entry = (h, start)
                result.append(entry)

            # Talking about python code being slow, the following code is an
            # alternative implementation.
            #
            # It complexity is better since is does a single traversal on the
            # bottomset. However since it is all python it end up being
            # slower.
            # I'm keeping it here as an inspiration for a future C version
            # branches = []
            # for current in reversed(bottomrevs):
            #     ps = parents(current, parentrevs)
            #     found = False
            #     for brevs, bexpect in branches:
            #         if current in bexpect:
            #             found = True
            #             brevs.append(current)
            #             bexpect.discard(current)
            #             bexpect.update(ps)
            #     if not found:
            #         branches.append(([current], set(ps)))
            # for revs, __ in reversed(branches):
            #     head = revs[0]
            #     index = self.depthrev(repo, head) - len(revs)
            #     result.append((head, index))

        # top part is trivial
        top = (rangeid[0], globalindex)
        result.append(top)
        return result

@eh.reposetup
def setupcache(ui, repo):

    class stablerangerepo(repo.__class__):

        @localrepo.unfilteredpropertycache
        def stablerange(self):
            return stablerange()

    repo.__class__ = stablerangerepo